The present invention relates generally to mobile towed machines of the type having a tongue swingable in relation to the machine frame about an approximately upright axis, thus providing adjustment of lateral offset between the machine and a towing vehicle as the combination advances and more particularly to means for controlling the pivoting of the tongue about the frame.
The general mode of operation of towed machines, such as harvesters including mower-conditioners and the like and having swingable tongues, is well known as is the particular portion of their operation in which adjustment is made between a transport position and an operating position. In the former the machine trails generally rearwardly behind the towing vehicle to keep overall transport width of the combination to a minimum while in an operating position, for example that of a harvester in a field of crop, the machine is offset rearwardly and to one side of a towing vehicle such as a tractor so that the tractor does not pass over the ground or crop material to be treated or harvested.
In many machines the swinging of the tongue in relation to the machine frame is effected by a hydraulic actuator such as a conventional piston-type hydraulic cylinder. Typically, the transport or carrying wheels of the machine are fixed (non-castering) so that realignment of the machine behind the towing vehicle can be made only as the combination advances, the hydraulic actuator acting in effect as a steering means permitting not only changing between particular operating and transport positions, but also, when a suitable control valve is provided for the actuator, adjustment over a range of positions, to suit particular operating and transport conditions.
It is desirable, particularly when transporting on a highway to be able to lock the tongue in relation to the machine frame so as to guard against accidental swinging of the machine from a position generally behind the towing vehicle into an offset position where it may collide with oncoming traffic or strike an obstruction beside the road. Such an accidental swinging could arise from inadvertent manipulation of the hydraulic actuator control or from a failure of the hydraulic system between the towing vehicle and the actuator causing a loss of hydraulic pressure and allowing the hydraulic actuator to float.
It is known to provide mechanical means to prevent the tongue of mobile towed machines from inadvertent swinging but such means typically suffer from the disadvantage of being limited by practical considerations to only one or a small number of spaced locked positions and manipulation of the locking device from an unlocked to a locked condition is often difficult. Before engaging the lock, the mating portions connected to the tongue and frame respectively may have to be precisely aligned by maneuvering of the machine, if it is connected to the towing vehicle, so as to cause relative pivoting between tongue and frame. Also, disengagement of such locks is often difficult because, for example, if the machine is stopped on uneven ground, there can be residual horizontal components of force on the wheels resulting in a turning or steering force on the machine and hence a load within the locking device hampering disengagement.
The engagement of a mechanical locking device may require an operator to be closely adjacent a machine when it is being steered or maneuvered to a position where it is possible to manually engage the locking device and consequently there is a danger of the operator being struck and injured by the machine or towing vehicle.